For connection between two semiconductor integrated circuits which make long-distance data transmissions between them, the arrays of pads on their respective semiconductor packaging substrates are interconnected through wires on a backplane board. The pads are connected with the semiconductor integrated circuits via through-holes (hereinafter abbreviated as “TH”). Since a signal sent from pads of the semiconductor packaging substrate connected with one of the semiconductor integrated circuits attenuates before it reaches pads of the semiconductor packaging substrate connected with the other semiconductor integrated circuit, it is necessary to suppress crosstalk with a signal sent from pads of the packaging substrate connected with the other semiconductor integrated circuit. In such transmissions, the magnitude of a signal received by each semiconductor integrated circuit is at least 20 dB smaller than when it is transmitted, so it is necessary to reduce crosstalk from a transmitted signal to −60 dB or less.
Techniques of reducing crosstalk that ground (hereinafter abbreviated as GND) voltage pads are disposed around pads connected with signal lines (hereinafter referred to as signal pads) are known (JP-A-2000-349192 and JP-A-Sho61 (1986)-005549). Also JP-A-Hei5 (1993)-206678 proposes a technique that five or more grounded through-holes (hereinafter abbreviated as GND TH) are disposed around a through-hole connected with each of the signal pads of a semiconductor packaging substrate (hereinafter referred to as signal TH) in order to reduce crosstalk and control characteristic impedance.